Magnetic resonance imaging (MRI) involves producing a magnetic field and producing radio frequency (RF) energy in the presence of a patient in the magnetic field. The patient may absorb some of this RF energy. Absorbing RF energy may cause tissue to heat up. Additionally, there may be other issues associated with magnetic fields, RF fields, and so on. Therefore various regulations, guidelines, and practicalities concern the specific absorption rate (SAR) of an MRI patient.
SAR may increase near conductors (e.g., wires) implanted in, transiting, lying on the surface of, or in contact with a patient. For example, the SAR may increase near a wire associated with an implanted pacemaker, near a wire associated with an implanted neurostimulator, near a bar being used to stabilize a fracture or other orthopaedic device, and so on. In some cases, a conductor may cause an unpredictable and unacceptable SAR increase in tissue near the conductor. Therefore, MRI may not be advisable or even available to patients having implanted wires. In some cases a conductor (e.g., wire) may experience a change in temperature of 30 degrees Centigrade in one second.
Understanding SAR depends on understanding the interaction between a field created by RF energy and a wire. Interactions between fields and conductors is controlled by the electric fields (E-fields) that accompany RF transmission. E-fields may induce a potential in a wire. One type of induction is described by:V=∫E*dx 
where the integral is taken over the path (x) of the wire.
Conventional attempts to control MRI related SAR in patients having implanted wires have included carefully arranging patients with respect to the MRI RF coil, using low-power RF pulses, and so on. However, these approaches may have produced sub-optimal results leaving some patients without the option and benefit of MRI diagnosis. With the increasing accuracy, sophistication, speed, and ubiquity of MRI, this is a serious drawback to those patients.